Threats to Pingao
In the “Pingao (or Pikao) the Golden Sand Sedge”
The threats to the continued existence of pingao are many and varied. In ecosystems where pingao still inhabits large areas the greatest threats are competition from the introduced plants marram grass and tree lupin, and browsing by stock, deer, rabbits and hares.
Threats and damage as a result of human recreation and coastal development tends not to be such a problem as many of the areas where these activities occur have already been largely denuded of pingao.
Marram grass (Ammophila arenaria) is an exotic sand-binder and dune builder and can be found on virtually every beach in New Zealand. It is a silvery green coloured perennial grass, native to Europe and has been widely introduced around the world as a dune stabiliser1.
New Zealand lies within marram's native latitudes of 30 to 63 degrees2 providing a temperate climate that it favours3. Marram suffers from a lack of vigour in warmer climates4 and this has been suggested as a reason why marram is more of a conservation management problem in the cooler southern areas of New Zealand5.
Marram requires active sand burial to stimulate growth (like pingao), and both species go moribund when sand movement is limited6. Unlike pingao however, marrram thrives under rapid burial1, surviving burial rates that would bury pingao, making marram a highly competitive plant. Consequently, marram tends to dominate areas that accumulate sand rapidly at the expense of pingao 7.
Those areas where pingao remains may be because they are areas receiving slower burial, which do not favour marram growth7.
Slower burial typically occurs with coarser particles as they are more difficult for the wind to transport7. Pingao may be found in areas that feature more coarse sand and gravel, such as Kaitorete Spit (south of Christchurch7 ). The exact location of marram or pingao dominated dunes will depend on the sand source, shape of the beach or embayment, and the direction of the prevailing wind7.
Marram's leaf structure and arrangement allows it to trap sand more efficiently than pingao7. It typically forms taller steeper dunes that are more densely vegetated, frequently exclude any other vegetation to form pure marram dunes3. Marram, although hardy1,8, may have a lower tolerance to salinity than pingao 9,10 which may be a factor that explains differences in pingao and marram-dominated dune systems.
Marram’s primary method of reproduction is vegetative rhizomes6 although it also produces seeds1. The rhizomes are extremely vigorous and can colonise new areas by breaking off (e.g. in a storm event). These fragmented rhizomes can remain viable after extended immersion in seawater1, enhancing their colonising abilities.
Marram's Interaction with pingao
Marram exludes pingao in two ways. First, due to marram's superior sand trapping abilities, it is able to deprive pingao of sand causing it to go moribund. Secondly, because marram grows quickly, developing extensive root and rhizome systems it is able to outcompete pingao for moisture, resulting in desiccation on pikao6,7. It has been suggested that this desiccation slows pingao’s growth, resulting in burial and death6,7.
Marram as a Conservation Problem
Both marram and tree lupin are regarded as important threats to pingao 11. The Department of Conservation has rated marram grass 12/12 on its effects on ecosystems, based on ratings for significant change to structure and/or composition of the community; suppression of regeneration of native species; persistence over time and whether it increases the fire hazard12. It has also ranked 18/21 on a biological success rating, based on maturation rate; seeding capacity; dispersal; establishment/growth; vegetative reproduction; competitive ability and resistance to management12.
Strategic management of marram is site-based and focuses on areas where there is a large pingao population with high site values.
To ensure their high biodiversity values are maintained, marram is controlled at several sites around New Zealand. The herbicide used is either Gallant or Hurricane. Application methods include helicopter, Argo and Knapsack.
Regardless of the methods used, repeated and intensive treatment will be required14,15. Both herbicides are grass-specific. and do not affect any other plant species. Unfortunately this means that the native grass species (such as the native sand tussock Austrofestuca littoralis) are susceptible to the herbicides used to control pingao and care is needed to avoid these plants. Research has shown that sand tussock has a substantial seed bank thus allowing natural regeneration of this species5.
Controlling marram ensures the natural geomorphic processes are set back in motion, the natural succession of plants will be re-established and the biota, function and character of the dunelands will be restored15.
Extensive research has been undertaken to understand the impact of marram removal on natural ecosystem processes. The research has found that over time natural processes are restored and native vegetation such as pingao increases in density.
Lupin (Lupinus aboreus) was introduced in conjunction with marram as it as nitrogen fixer to provide a nutrient source for marram allowing it to remain vigorous17. Lupin also negatively interacts with pingao by shading it out18. Because lupin usually occurs with marram, it means that pingao will often face a multitude of competitive pressures, severely hampering its ability to persist.
In the late 1980's lupin in New Zealand suffered an infection by lupin blight, severely affecting the population and offering pingao a respite17. Although lupin has recovered to some extent, the Forest Research has been investigating other nitrogen fixing alternatives, which may see the introduction of further threats from other exotic species to the dune environment19. Moves such as this should proceed with caution and be considered a threat to pingao and other coastal species until proven otherwise. An awareness of this issue should be sought by those managing pingao recovery so they may stay abreast of developments in this area.
The negative impacts of stock have been noted as far back as 1880's20. Stock was observed damaging the structural integrity of pingao dunes, opening them up to erosion and blowouts and requiring the introduction of marram and lupin as measures to protect against this17,20. Fencing of areas of pingao vulnerable is the only management measure that can protect pingao from tramping. Frequently these areas are located on private land (such as in the Catlins), so fencing costs may be meet by the land-owner, although they may instead have to be funded by a coast care organisation or DOC.
Rabbits and hares21,22 and possums18 have both been noted browsing pingao. Plants particularly vulnerable to browse are young plants and pose a major threat to revegetation projects. It appears that older plants (after first flowering) are no longer platable23. Sheep have also been noted browsing pingao, but only when there was no other vegetation available22.
Preliminary investigations are underway to examine the effectiveness of an animal repellent to discourage browsing. This repellent (Treepel) has already been found to be effective for rabbits, possums and hares on pine seedlings24.
Pikao that is threatened by coastal development may be best managed by the RMA3,17 and the associated generation of Regional and District Plans (via identification of sensitive areas that contain stands of pingao). An awareness by local territorial authorities will also need to be exercised when any coastal amenities etc. are developed to ensure areas of pingao are not adversely affected.
Damage can also be attributed to recreational activities. Particularly 4 wheel driving and trail biking, which can badly damage otherwise healthy pingao stands. These activities also exacerbate erosion problems by damaging the structural integrity of the dunes and pingao ability to trap sand by damaging the plant. Bonfires, barbecues and cigarette stubs all pose a fire risk that threaten pingao stands and people not restricting themselves to walkways causes erosion problems that threaten to bury or expose and desiccate pingao plants.
- Pickart A. J. and Saywer J. (1998). Ecology and restoration of Northern California Coastal dunes. California Native Plant Society. 152p.
- Huiskes 1979 cited by Pickart A. J. and Saywer J. (1998). Ecology and restoration of Northern California Coastal dunes. California Native Plant Society. 152p.
- Bergin, D. O., FitzSimons, P., Freeman, C., Herbert, J. W. and Kesby, N. A. (1997). Managment of Marram Grass in the Resoration of Indigenous Coastal Dune Vegetation in Australia and New Zealand. Paper accepted for The Pacific Coasts and Parks Conference, 7-11 Sept. Christchurch, New Zealand.
- Kerby 1986 cited by Bergin, D. O., FitzSimons, P., Freeman, C., Herbert, J. W. and Kesby, N. A. (1997). Managment of Marram Grass in the Resoration of Indigenous Coastal Dune Vegetation in Australia and New Zealand. Paper accepted for The Pacific Coasts and Parks Conference, 7-11 Sept. Christchurch, New Zealand.
- Jul. A.. Hilton, M. and Henderson, R. (1999). Patterns and Processes of Marram Invasion Mason Bay, Stewart Island and Recommendations for Marram Management. Department of Geography, University of Otago, Dunedin.
- DoC (1995). The interaction between Marram and Pingao on Sand Dunes. Completion of Permanent Plot Studies. Science for Conservation, 3. Department of Conservation.
- DoC (1992). Pingao Recovery Plan. Otago Conservancy 1993-1998. Department of Conservation, Dunedin.
- Timmins. S. M. and MacKenzie I. W. (1995). Weeds in New Zealand Protected Natural Areas Database. Department of Conservation Technical Series No. 8. Department of Conservation, Wellington.
- Esler, A. E. (1970) Manawatu sand dune vegetation. Proceedings of the New Zealand Ecological Society 17, 41-46.
- Sykes, M. T. and Wilson, J. B. (1989). The effect of salinity on growth of some New Zealand sand dune species. Acta Botanica Neerlandica, 38(2), 173-182.
- DoC (1998a). The impact of weeds on threatened plants. Science and Research Internal Report No. 164. Department of Conservation, Wellington.
- DoC (1997). Ecology and management of invasive weeds. Conservation sciences Publication No. 7. Department of Conservation, Wellington.
- DoC (1998b). Department of Conservation Strategic Plan for Managing Invasive Weeds. Department of Conservation, Wellington.
- Pickart, A. J. (1997). Control of European Beachgrass (Ammophila arenaria) on the West Coast of the United States. California Exotic Pest Plant Council Symposium 1997.
- Hilton, M. (2000). Marram Control in Southern New Zealand. Paper presented at the Coastal Dune Vegetation Network conference, Brighton, Christchurch, New Zealand.
- Moore, L. B. and Adams, N. M. (1963). Plants of the New Zealand Coast. Paul's Arcade, Hamilton and Auckland.
- Bergin, D. O. and Herbert, J. W. (1994). Resoration of native plant communities on sand dunes in New Zealand. Paper for the Forth Annual New South Wales Coastal Management Conference, 18-20 Oct, Gosford, Australia.
- D. Nelson (pers. comm.). Department of Conservation, Coastal Otago Area Office, Dunedin.
- Gadgil, R. L., Sandberg, A. M. and Lowe, A. T. (1999). Two seedling rooting media and subsequent growth of a N-fixing plants in a New Zealand coastal sand-dune environment. New Zealand Journal of Forestry Science, 29(2), 195-202.
- Thomas, M. G. (1944). A Pakeha's recollections. The reminicences of Murray Gladstone Thomas. Extracts relating to early Dunedin. Eccles, A. (ed). A. H. & A. W. Reed.
- Bergin, D.O. and Herbert, J. W. (1998). Pingao on Coastal sand dunes. Guidelines for seed collection, propagation and establishment. CDVN Technical Bulletin No. 1. Forest Research Institute, Rotorua.
- Courtney, S. P. (1983). Aspects of the ecology of Desmochoenus spiralis (A. Rich.) Hook. f. Unpublished MSc Thesis. University of Canterbury, New Zealand.
- P.Pope (pers. comm.) Reserves Officer, Dunedin City Council, Dunedin, New Zealand.
- FRI (1988). Animal Repellents for tree seedlings. What's new in Forest Research. No. 162. New Zealand Forest Research Institute.